NOx reduction compositions for use in FCC processes

ABSTRACT

Compositions comprising a component containing (i) an acidic oxide support, (ii) an alkali metal and/or alkaline earth metal or mixtures thereof, (iii) a transition metal oxide having oxygen storage capability, and (iv) a transition metal selected from Groups Ib and/or IIb of the Periodic Table provide NO x  control performance in FCC processes. The acidic oxide support preferably contains silica alumina. Ceria is the preferred oxygen storage oxide. Cu and Ag are preferred Group I/IIb transition metals. The compositions are especially useful in the cracking of hydrocarbon feedstocks having above average nitrogen content.

This application is a continuation of U.S. Ser. No. 08/848,354, filedApr. 28, 1997, now U.S. Pat. No. 6,143,167 which is a continuation ofU.S. Ser. No. 08/473,462 filed Jun. 7, 1995 now abandoned, which is acontinuation of U.S. Ser. No. 08/437,123 filed May 5, 1995, nowabandoned.

BACKGROUND OF THE INVENTION

Public policy and cost/benefit pressures have created an increasingdesire to reduce the amount of polluting gases released by industrialprocesses. As a result, there has been a drive to find ways ofdecreasing pollution by modifying industrial processes.

In the petroleum refining industry, fluid catalytic cracking (FCC) ofhydrocarbons is a commonly used petroleum refining method. In an FCCprocess, catalyst particles (inventory) are repeatedly circulatedbetween a catalytic cracking zone and a catalyst regeneration zone. Inregeneration, coke deposits (from the cracking reaction) on the catalystparticles are removed at elevated temperatures by oxidation. The removalof coke deposits restores the activity of the catalyst particles to thepoint where they can be reused in the cracking reaction.

While FCC processes are efficient from the point of catalyst use, theregeneration step typically results in the evolution of undesirablegases such as SO_(x), CO, and NO_(x). Various attempts have been made tolimit the amounts of these gases created during the FCC regenerationstep or otherwise to deal with the gases after their formation. Mosttypically, additives have been used either as an integral part of theFCC catalyst particles themselves or as separate admixture particles inthe FCC catalyst inventory in attempts to deal with these problematicgases. For example, magnesium aluminate spinel additives are often usedto prevent or minimize emission of SO_(x) from the regenerator. Variousnoble metal catalysts have been used to minimize the emission of CO fromthe regenerator.

Unfortunately, the additives used to control CO emissions typicallycause a dramatic increase (e.g., 300%) in NO_(x) evolution from theregenerator. Some of the spinel-based (SO_(x) reduction) additives actto lessen the amount of NO_(x) emission, but with limited success. Thus,there remains a need for more effective NO_(x) control additivessuitable for use in FCC processes.

SUMMARY OF THE INVENTION

The invention provides compositions suitable for use in FCC processeswhich are capable of providing superior NO_(x) control performance.

In one aspect, the invention provides compositions for reducing NO_(x)emissions in FCC processes, the compositions comprising a componentcontaining (i) an acidic oxide support, (ii) an alkali metal and/oralkaline earth metal or mixtures thereof, (iii) a transition metal oxidehaving oxygen storage capability, and (iv) a transition metal selectedfrom Groups Ib and/or IIb of the Periodic Table. The acidic oxidesupport preferably contains silica alumina. Ceria is the preferredoxygen storage oxide. Cu and Ag are preferred Group I/IIb transitionmetals.

In another aspect, the invention encompasses FCC processes using theNO_(x) reduction compositions of the invention either as an integralpart of the FCC catalyst particles themselves or as separate admixtureparticles in the FCC catalyst inventory.

These and other aspects of the invention are described in further detailbelow.

DETAILED DESCRIPTION OF THE INVENTION

The invention encompasses the discovery that certain classes ofcompositions are very effective for the reduction of NO_(x) gasemissions in FCC processes. The NO_(x) reduction compositions of theinvention are characterized in that they comprise a component containing(i) an acidic oxide support, (ii) an alkali metal and/or alkaline earthmetal or mixtures thereof, (iii) a transition metal oxide having oxygenstorage capability, and (iv) a transition metal selected from Groups Iband/or IIb of the Periodic Table.

The acidic oxide support should be of sufficient acidity for thecomposition to act as an effective NO_(x) reduction additive. Thesupport preferably contains acidic silanol or bridged hydroxyl groups.These acid groups are preferably characterized by NMR shifts in theregion of −90 to −100 ppm compared to a TMS (trimethyl silane) standard.The support may be crystalline or amorphous. Preferably, the acidicoxide support contains at least some alumina. More preferably, the oxidesupport contains at least 50 wt. % alumina. The oxide support ispreferably an oxide selected from the group consisting of alumina,silica alumina, and lanthana alumina. Amorphous silica aluminas are mostpreferred. Where an amorphous silica alumina support is used, thesupport preferably has an alumina to silica molar ratio of about 3-50:1.

The acidic oxide support further preferably has sufficient surface areato promote the NO_(x) reduction process. Preferably, the oxide supporthas a surface area of at least 50 m²/g, more preferably about 70-200m²/g.

The alkali and/or alkaline earth metal may be any alkali metal, alkalineearth metal or combinations thereof The NO_(x) reduction componentpreferably contains an alkali metal selected from sodium, potassium andmixtures thereof. The amount of alkali/alkaline earth metal present inthe NO_(x) reduction component of the invention is preferably about 1-10parts by weight (measured as alkali/alkaline earth metal oxide) per 100parts by weight of the oxide support material. While the alkali/alkalineearth metal content is expressed as the amount of corresponding oxide,preferably the alkali/alkaline metal is present in cationic form ratherthan as discrete oxide.

The transition metal oxide having oxygen storage capability may be anytransition metal oxide having oxygen storage capability similar to thatof ceria. Preferably, at least a portion of the oxygen storage oxide isceria. More preferably, the oxygen storage oxide consists essentially ofceria. Other non-stoichiometric metal oxides having known oxygen storagecapability may also be used. The oxygen storage oxide is preferablypresent as a microdispersed phase as opposed to large bulk oxideparticles or ions located at exchange sites in the oxide support. Theamount of the oxygen storage oxide present in the NO_(x) reductioncomponent may be varied considerably relative to the amount of acidicoxide support. Preferably, the NO_(x) reduction component contains atleast about 1 part by weight of oxygen storage oxide per 100 parts byweight of the oxide support material, more preferably at least about2-50 parts by weight per 100 parts of the oxide support material.

The Group Ib and/or IIb transition metal may be any metal or combinationof metals selected from those groups of the Periodic Table. Preferably,the transition metal is selected from the group consisting of Cu, Ag andmixtures thereof. The amount of transition metal present is preferablyat least about 100 parts by weight (measured as metal oxide) per millionparts of the oxide support material, more preferably about 0.1-5 partsby weight per 100 parts of the oxide support material.

The NO_(x) reduction component may contain minor amounts of othermaterials which preferably do not adversely affect the NO_(x) reductionfunction in a significant way. More preferably, however, the NO_(x)reduction component consists essentially of items (i)-(iv) mentionedabove. Where the composition of the invention is used as an additiveparticle for an FCC process, the NO_(x) reduction component may becombined with fillers (e.g. clay, silica, alumina or silica aluminaparticles) and/or binders (e.g. silica sol, alumina sol, silica aluminasol, etc.) to form particles suitable for use in an FCC process.Preferably, any added binders or fillers used do not significantlyadversely affect the performance of the NO_(x) reduction component.

Where the NO_(x) reduction composition is used as an additiveparticulate (as opposed to being integrated into the FCC catalystparticles themselves), the amount of NO_(x) reduction component in theadditive particles is preferably at least 50 wt. %, more preferably atleast 75 wt. %. Most preferably, the additive particles consist entirelyof the NO_(x) reduction component. The additive particles are preferablyof a size suitable for circulation with the catalyst inventory in an FCCprocess. The additive particles preferably have an average particle sizeof about 20-200 μm. The additive particles preferably have a Davisonattrition index (DI) value of about 0-45, more preferably about 0-15.

If desired, the NO_(x) reduction composition of the invention may beintegrated into the FCC catalyst particles themselves. In such case, anyconventional FCC catalyst particle components may be used in combinationwith the NO_(x) reduction composition of the invention. If integratedinto the FCC catalyst particles, the NO_(x) reduction composition of theinvention is preferably represents at least about 0.02 wt. % of the FCCcatalyst particle, more preferably about 0.1-10 wt. %.

While the invention is not limited to any particular method ofmanufacture, the NO_(x) reduction component of the invention ispreferably made by the following procedure:

(a) impregnate the acidic oxide porous support particles with analkali/alkaline earth metal oxide source and an oxygen storage oxidesource to achieve the desired alkali/alkaline earth metal and oxygenstorage oxide content,

(b) calcine the impregnated support of step (a),

(c) impregnate the calcined support from step (b) with a source of GroupIb and/or IIb metal, and

(d) calcine the impregnated support from step (c).

The sources of alkali/alkaline earth metal oxide and oxygen storageoxide are preferably slurries, sols and/or solutions of the metal oxidesthemselves or salts of the respective metals which decompose to oxideson calcination or combinations of oxides and salts. If desired, theindividual constituents may be separately added to the support particleswith a calcination step in between each addition. If desired, theimpregnated particles are spray dried before the calcination of step(d). The calcination steps are preferably performed at about 450-750° C.

The NO_(x) reduction component may be used as a separate additiveparticle or as an integral part of an FCC catalyst particle. If used asan additive, the NO_(x) reduction component may itself be formed intoparticles suitable for use in an FCC process. Alternatively, the NO_(x)reduction component may be combined with binders, fillers, etc. by anyconventional technique. See for example, the process described in U.S.Pat. No. 5,194,413, the disclosure of which is incorporated herein byreference.

Where the NO_(x) reduction component of the invention is integrated intoan FCC catalyst particle, preferably the component is first formed andthen combined with the other constituents which make up the FCC catalystparticle. Incorporation of the NO_(x) reduction component directly intoFCC catalyst particles may be accomplished by an known technique.Example of suitable techniques for this purpose are disclosed in U.S.Pat. Nos. 3,957,689; 4,499,197; 4,542,188 and 4,458,623, the disclosuresof which are incorporated herein by reference.

The compositions of the invention may be used in any conventional FCCprocess. Typical FCC processes are conducted reaction temperatures of450 to 650° C. with catalyst regeneration temperatures of 600 to 850° C.The compositions of the invention may be used in FCC processing of anytypical hydrocarbon feedstock. Preferably, the compositions of theinvention are used in FCC processes involving the cracking ofhydrocarbon feedstocks which contain above average amounts of nitrogen,especially residual feedstocks or feedstocks having a nitrogen contentof at least 0.1 wt. %. The amount of the NO_(x) reduction component ofthe invention used may vary depending on the specific FCC process.Preferably, the amount of NO_(x) reduction component used (in thecirculating inventory) is about 0.1-15 wt. % based on the weight of theFCC catalyst in the circulating catalyst inventory. The presence of thecompositions of the invention during the FCC process catalystregeneration step dramatically reduces the level of NO_(x) emittedduring regeneration.

EXAMPLE 1

An amorphous silica alumina particulate support containing 6 wt. %silica was impregnated with a sodium carbonate solution, dried andcalcined to achieve a 3.6 wt. % Na content measured as Na₂O based on theweight of the silica alumina. The Na-containing silica alumina particleswere then impregnated with a solution of cerium nitrate and then driedto achieve a ceria content of about 1 wt. % based on the weight of thesilica alumina particles. The Ce-containing composition was thenimpregnated with a silver nitrate solution to achieve a silver contentof about 5 wt. % (oxide basis) based on the weight of the silica aluminaparticles. The impregnated particles were then dried and calcined atabout 704° C. to form a particulate composition in accordance with theinvention.

EXAMPLE 2

An amorphous silica alumina particulate support containing 6 wt. %silica was impregnated with a sodium carbonate solution, dried andcalcined to achieve a 6 wt. % Na content measured as Na₂O based on theweight of the silica alumina. The Na-containing silica alumina particleswere then impregnated with a solution of cerium nitrate and then driedto achieve a ceria content of about 22 wt. % based on the weight of thesilica alumina particles. The Ce-containing composition was thenimpregnated with a copper nitrate solution to achieve a copper contentof about 2 wt. % (oxide basis) based on the weight of the silica aluminaparticles. The impregnated particles were then dried and calcined atabout 704° C. to form a particulate composition in accordance with theinvention.

EXAMPLE 3

The 152 g of the composition of example 1 was admixed with 2908 grams ofa commercial FCC catalyst (Grace Davison Orion® 842 equilibrium catalyst(ECAT)) and 10 g of a combustion promoter (Grace Davison CP-5). Theadmixture was then used to crack a hydrocarbon feedstock containing 0.3wt. % nitrogen in a DCR pilot plant FCC unit. The cracking was performedat a 75% conversion rate and 1000 g/hr catalyst feed rate. As a controlexample, the same catalyst admixture was run without the composition ofexample 1. The NO_(x) emission measured from the FCC unit regeneratorwas 65% less when the composition of example 1 was used compared to thecontrol example.

EXAMPLE 4

The 10 g of the composition of example 2 was admixed with 2000 grams ofa commercial FCC catalyst (Grace Davison Orion® 922G ECAT) and 5 g of acombustion promoter (Grace Davison CP-5). The admixture was then used tocrack a Countrymark hydrocarbon feedstock (0.13 wt. % N) in an FCC pilotplant (DCR) unit. The cracking was performed at a 75% conversion rateand 1000 g/hr catalyst feed rate. As a control example, the samecatalyst admixture was run without the composition of example 2. TheNO_(x) emission measured from the FCC unit regenerator was 46% less whenthe composition of example 2 was used compared to the control example.

What is claimed is:
 1. A NOx removal composition suitable for reducingNOx emissions in the presence of a CO oxidation promoter during catalystregeneration in a fluid catalytic cracking process, said compositioncomprising particles having a particle size of about 20-200 μm andcomprising (i) an acidic oxide support containing at least 50 wt %alumina, (ii) about 1-10 parts by weight of magnesium oxide; (iii) atleast 1 part by weight of CeO₂ and (iv) about 0.01-5.0 parts by weight,measured as metal oxide, of a transition metal selected from Group Ib ofthe Periodic Table, all of said parts by weight being per 100 parts byweight of said acidic oxide support material.
 2. The composition ofclaim 1 wherein said acidic oxide support is selected from the groupconsisting of alumina, silica alumina and lanthana alumina.
 3. Thecomposition of claim 2 wherein said acidic oxide support is silicaalumina.
 4. The composition of claim 3 wherein said silica alumina isamorphous silica alumina.
 5. The composition of claim 3 wherein saidsilica alumina has an alumina:silica mole ratio of about 3-50:1.
 6. Thecomposition of claim 1 wherein said composition contains about 2 to 50parts by weight of CeO₂ per 100 parts by weight of said acidic oxidesupport material.
 7. The composition of claim 1 wherein said Group Ibtransition metal is selected from the group consisting of copper, silverand mixtures thereof.
 8. A fluid cracking catalyst comprising (a) acracking component suitable for catalyzing the cracking of hydrocarbons,and (b) a NOx reduction component comprising (i) an acidic oxide supportcontaining at least 50 wt % alumina, (ii) about 1-10 parts by weight ofmagnesium oxide; (iii) at least 1 part by weight of a CeO₂, and (iv)0.01-5.0 parts by weight total, measured as metal oxide, of a transitionmetal selected from Group Ib of the Periodic Table, all of said parts byweight being per 100 parts by weight of said acidic oxide supportmaterial, said NOx reduction components comprising particles having aparticle size of 20-200 μm and being present in the cracking catalyst ina sufficient NOx reducing amount.
 9. The cracking catalyst of claim 8wherein said cracking catalyst comprises an admixture of component (a)and component (b).
 10. The cracking catalyst of claim 8 wherein saidcatalyst comprises integral particles which contain both components (a)and (b).
 11. The cracking catalyst of claim 8 wherein the NOx reductioncomponent (b) comprises about 0.1 to 15 wt % of the cracking catalyst.12. A method of reducing NOx emissions in the presence of CO oxidationpromoters during fluid cracking of a hydrocarbon feedstock into lowermolecular weight components, said method comprising contacting ahydrocarbon feedstock with a cracking catalyst at elevated temperaturewhereby lower molecular weight hydrocarbon components are formed, saidcracking catalyst comprising (a) a cracking component suitable forcatalyzing the cracking of hydrocarbons, and (b) a NOx reductioncomponent comprising (i) an acidic oxide support containing at least 50wt % alumina, (ii) about 1-10 parts by weigh of magnesium oxide; (iii)at least 1 part by weight of a CeO₂, and (iv) 0.01-5.0 parts by weighttotal, measured as metal oxide, of a transition metal selected fromGroup Ib of the Periodic Table, all of said parts by weight being per100 parts by weight of said acidic oxide support material, said NOxreduction components comprising particles having a particle size of20-200 μm and being present in the cracking catalyst in a sufficient NOxreducing amount.
 13. The method of claim 12 wherein said crackingcatalyst is fluidized during contacting said hydrocarbon feedstock. 14.The method of claim 12 further comprising recovering used crackingcatalyst from said contacting step and treating said used catalyst underconditions to regenerate said catalyst.
 15. The method of claim 12wherein said hydrocarbon feedstock contains at least 0.1 wt % nitrogen.16. The method of claim 12 wherein the hydrocarbons are cracked in thepresence of at least one CO combustion promoter.